In recent years the development of high data rate generation well logging instruments such as multiple transducer, high frequency acoustic logging instruments and multiple channel high frequency electric logging instruments together with fast count rate nuclear well logging instruments of the gamma ray spectroscopy type in the well logging industry have generated the necessity for wider bandwidth well logging cables. A solution to the bandwidth problem in a well logging cable is to employ a cable having electrical conductors to supply power from the surface to downhole instrumentation suspended on the cable while simultaneously employing one or more optical fibers in the logging cable for transmitting high speed wide-band data from the downhole instrument to the surface.
Slip ring arrangements have been commonly used in the art of well logging to take signals from the logging cable on the rotating cable drum and conduct them into the well logging truck. If a well logging truck employing a logging cable having one or more optical fibers is similarly employed in a well logging environment, then the well logging system must be capable of also removing cable signals from the rotating cable drum from the optical fibers and supplying these signals to the well logging truck instrumention for translation and processing. Thus it is apparent that an optical analog of the typical slip joint used for translating electrical signals from the rotating cable drum into the truck is of interest in the well logging environment.
Optical rotary joints enable communication between rotating and stationary systems employing optical fibers in such fiber optic communication systems. Commercially available low loss, passive optical rotary joints for single channel communication only have been developed in the past. Two channel optical rotary joint devices have been constructed which have losses on the order of 5 db for the optical rotary joint. A primary difficulty with commercially available multi-channel optical rotary joint systems is that such systems have involved mechanically sensitive arrangements of prisms, lenses, mirrors and optical masks which makes them too delicate to employ in a well logging environment where up to 30,000 feet of well logging cable may be spooled on a large drum on the back of a well logging truck and which is utilized outdoors under extremely adverse environmental conditions and all types of weather. Thus it would be desirable to have a rugged, reliable and simple passive optical rotary joint which is suitable for use in a well logging environment.